Piping systems and other associated components such as valves, pumps, and steam generators represent a large part of the investment in a power generating station. The effects of a seismic event or other sudden shock load on unprotected or inadquately protected systems can be very costly. Thus it has been necessary to provide shock arresters to control such motion by locating a load-carrying member between the piping or other system and adjacent support structure the instant a load sufficient to cause abnormal motion is initiated. The potentially damaging motion is arrested before it develops. However, for normal, thermal motion the arrester telescopes freely in either direction through its operating stroke.
Previously, hydraulic shock arrestors offered the primary solution to the problem of restraining piping systems and associated components from damage resulting from earthquakes and other shocks while enabling unrestricted movement for thermal motion. Because hydraulic shock arresters are affected by radiation and have other shortcomings, all mechanical shock arresters have been developed.
U.S. Pat. No. 3,876,040, for example, discloses acceleration-sensitive motion snubber that has been widely used. In the system of that patent, reciprocating strut movement is converted to rotary motion and such motion is used to rotate an inertia mass through a coil spring, which also functions as a brake when the inertia of the mass introduces a lagging force. U.S. Pat. No. 4,103,760 produces some improvements to the system shown in the earlier patent, including a pair of inertia masses interconnected by a coil spring. These systems have proven to be highly sensitive and reliable. Nevertheless, requirements have been established for testing the operation of the motion snubbing mechanism periodically after a strut is installed in its working environment in a power generating station. It is a costly and time-consuming procedure to remove a strut and take it to a test station in that some of the struts are quite large and heavy, and many of the struts are mounted in locations that are not easily accessible. Thus, it is desirable that the motion snubbing mechanism be capable of being tested without removing the strut. Some advances have been made in this direction, but a need still exists for an improved strut that will permit simple in-place testing.
The systems described in the above-mentioned patents are acceleration responsive, which means that they will permit a slow increase of velocity. Such increasing velocity could be damaging to a strut if it is improperly handled, and thus other means have been provided to offset this. Thus it is desirable that the motion snubbing mechanism limit velocity to a predetermined maximum but permit the strut to telescope freely in either direction through its operating stroke for normal, thermal motion.